Peter Kenyon, TunnelTalk

Sydney announced yesterday (April 4), that it expects to procure four TBMs, of about 7.6m diameter, to complete the city's ambitious Aust$8.5 billion (US$8.9 billion) Skytrain Project.

Sydney's North West Rail Link includes 30 km of tunnels

In the first of two environmental impact assessments the New South Wales State Government unveiled detailed plans of the proposed 15km twin 6.6m i.d. running tunnels that comprise the majority of the 23km heavy rail alignment linking Epping with Sydney's northwest district near Rouse Hill. From the new Epping interchange station commuters will be able to use existing rail services to complete their journey to the centre of Sydney.

The first statement, based on designs and alignments drawn up by a consortium headed by AECOM and including Parsons Brinckerhoff (Australia), concentrates on 15km of tunnelling and subsurface excavations.

Planners in New South Wales want to speed up the process of procuring the needed TBMs by seeking approval on that element of the project first. A second impact assessment on the design of eight new stations and the rail infrastructure will be completed later this year.

New line links Sydney's north west to the centre

Five of the stations – Cherrybrook, Castle Hill, Hills Centre, Norwest and Bella Vista will be underground, with TBMs 1 and 2 launching on their 6km drives east from Cherrybrook to the existing interchange station at Epping in late 2014 and early 2015.

TBMs 3 and 4 are scheduled for their 9km eastbound drives from the Bella Vista station box to Cherrybrook at the same time as TBMs 1 and 2 begin their drives, meaning that all four TBMs will be working simultaneously for approximately six months. Hills Centre station box will act as a maintenance post before the TBMs restart their westward drive to Cherrybrook.

Kellyville and Rouse Hill stations will be elevated, while the western terminus at Cudgegong Road station will be built into an excavated cutting. Early construction tenders for surface works and station excavations are scheduled to begin in 2013, with the TBMs delivered in 2014.

Up to 4km of the alignment will be on elevated track, which has earned the North West Rail Project the label 'Skytrain'.

The continuous 15km of twin segmentally lined running tunnels, run from Epping Station to a tunnel portal just north of Celebration Drive at Bella Vista.

Topography along the corridor varies greatly, particularly near creeks and watercourses, and tunnel depths will vary depending on proximity to stations and geological constraints along the corridor.

Proposed 23km North West Rail alignment

Four 7.6m diameter TBMs will carry out six drives

Geological surveys reveal that rock conditions on the alignment will be about 60% through Hawkesbury Sandstone and the remainder through shale.

The tunnel crown ranges in depth from 5m-70m below ground level but will be typically 20m-25m deep. Connecting cross passages will be constructed by roadheaders at 240m intervals.

The North West Rail Link is projected to attract 29 million trips/year within five years of opening in 2019. The project is expected to create 16,200 jobs, and is designed to cut commuting times from the northwest area of Sydney to the city centre by up to 40 minutes. Population in the region is expected to grow by 200,000 to more than 600,000 over the next 40 years, according to State Government projections.

Planning permission was lodged in December last year, and the first phase of public consultation ends on May 21, 2012.

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